FIG. 1 schematically shows a typical onshore hydrocarbon well location and surface equipments SE above a hydrocarbon geological formation GF after drilling operation has been carried out, after a casing string CS has been run and after cementing operations have been carried out for sealing the annulus CA (i.e. the space between the well-bore WB and the casing string CS).
Typically, the casing string CS comprises a plurality of casing joints CJ, two casing joints being coupled together by a casing collar CC. The casing string function is to stabilize the well-bore.
The casing joint CJ is a length of steel pipe, generally around 13 m or 40 ft long with an externally threaded (male thread form) connection at each end. Casing joints are assembled to form a casing string of the correct length and specification for the well-bore in which it is installed.
The casing collar CC is an internally threaded (female thread form) short length of pipe used to connect two casing joints. The resulting connection must provide adequate mechanical strength to enable the casing string to be run and cemented in place. The casing collar must also provide sufficient hydraulic isolation under the design conditions determined by internal and external pressure conditions and fluid characteristics.
The casing may be made of plain carbon steel, stainless steel or other material in order to withstand a variety of forces, such as collapse, burst, and tensile failure, as well as chemically aggressive fluid. Nevertheless, in harsh environment, the casing may be subject to corrosion that may affect its functionality.
At this stage, well logging operation may be carried out. The well logging operation serves to measure various parameters of the hydrocarbon well geological formation (e.g. resistivity, porosity, etc. . . . at different depths) and in the well-bore (e.g. temperature, pressure, fluid type, fluid flowrate, etc. . . . at different depths). Such measurements are performed by a logging tool TL. Generally, a logging tool comprises at least one sensor (e.g. resistivity sonde, mechanical sonde, gamma ray neutron sonde, accelerometer, pressure sensor, temperature sensor, etc. . . . ) and measures at least one parameter. It may include a plurality of same or different sensors sensitive to one or more parameters. The logging tool is moved up and down in the borehole for gathering data about the various parameters by means of a cable LN. The cable may be a mechanical cable, an electrical cable or an electro-optical cable comprising a fiber line protected against potential harsh environment existing in the well-bore. The mechanical, electrical, or electro-optical cable transmits electrical signals or optical signals from the logging tool to the surface unit.
The logging tool may be deployed inside the well-bore by an adapted surface equipment SE that may include a vehicle SU and an adapted deploying system, e.g. a drilling rig DR or the like. Data related to the hydrocarbon geological formation GF or to the well-bore WB gathered by the logging tool TL may be transmitted in real-time to the surface, for example to the vehicle fitted with an appropriate data collection and analysis computer and software.
In particular, a logging tool TL may comprise a casing collar locator tool. Such a locator is used to confirm or correlate depth by using known reference points on the casing string. A known casing collar locator is an electrical logging tool that detects the known casing features such as pup joints installed for correlation purposes (measurement of the voltage across a spool in the presence of magnet). The casing collar locator tool provides a casing collar log that generally incorporates a gamma ray log to correlate the relative position of casing string features, such as the location of a particular pup joint, with the reservoir or formation of interest. Such a locator lacks of sensitivity in particular in casing having an important diameter.